In general, high-contrast photographic images are used for the formation of character images or color separation halftone dot images in the photomechanical process or for the formation of finely detailed line drawing images in the super-high resolution photomechanical process. Accordingly, certain silver halide photographic materials for use in such processes are known to be capable of forming very high-contrast photographic images.
There is a conventional image-forming method in which a light-sensitive material comprised of a silver chlorobromide emulsion whose silver halide grains have an average grain size of, for example, 0.2 .mu.m, a narrow grain size distribution and uniform configuration and whose silver chloride content is as high as at least 50 mole % is processed in an alkaline hydro-quinone developer solution having a low sulfite ion concentration to thereby obtain high-contrast, high-sharpness and high-resolution images such as, e.g., halftone dot or fine line drawing images.
Silver halide light-sensitive materials of such the kind are known as lith-type light-sensitive materials.
The photomechanical process includes a process for converting a continuous-tone original image into a halftone dot image, i.e., the process for converting changes in the density of the continuous tone of an original into an assemblage of dots having areas proportional to the respective densities.
In this process, the above-mentioned lith-type light-sensitive material is used, exposed through a crossline screen or contact screen to an original image, and then developed, whereby a halftone dot image is formed.
To accomplish this, a silver halide light-sensitive photographic material having a fine-grained silver halide emulsion comprising silver halide grains uniform in the grain size as well as in the grain configuration is used, but even when a light-sensitive material of this kind is used, if processed in a developer solution for general black-and-white developing use, the obtained results will be inferior in the halftone dot image formation to those obtained when processed in a lith-type developer solution. Therefore, the light-sensitive material should be processed in a lith-type developer solution of a single hydroquinone developing agent and an extremely low sulfite ion concentration. However, the lith-type developer solution, since its preservability is very poor due to its proneness to undergo autoxidation, essentially needs a control method to keep its developing quality constant even when used continuously over a long period. Every effort has hitherto been made to improve the preservability of this developer solution.
As for the improvement, a replenishing method which, in order to retain the lith-type developer solution's preservability, separately uses both a replenisher to make up for the deterioration of the solution's activity due to development (processing fatigue replenishment) and a replenisher to make up for the exhaustion of the solution due to its autoxidation in time (spontaneous fatigue replenishment), the so-called two-liquid separately replenishing method, is generally widely employed in automatic processors for photomechanical process use. The above method, however, has the disadvantage that it requires control of replenishing balance of the two liquids, thus complicating the processor as well as its operation.
Also, the lith-type developer solution is unable to quickly provide processed images because it takes time (introduction period) until when an image begins to appear in its developing process.
On the other hand, methods for obtaining rapidly high contrast images without using the above-mentioned lith-type developer solution are known, which comprise incorporation of a hydrazine compound into a silver halide light-sensitive material as described in, e.g., U.S. Pat. No. 2,419,975, Japanese Patent Publication Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publication) Nos. 16623/1976 and 20921/1976. According to these methods, the sulfite ion concentration can be maintained high in a developer solution, so that processing can take place in a developer solution with its preservability being raised. However, any of these methods requires the use of a fairly high pH having developer solution in order to give a high-contrast image, so that they come into question in respect of the developer solution's stability if they are to be used as the technique to provide high-sensitivity images rapidly. Also, this developer solution has another disadvantage that its pH is so high as to tend to fog the light-sensitive material in processing, motivating the incorporation of various organic antifoggants in a high concentration into the solution, thus resulting in the sacrifice of the sensitivity.